Periodontitis causes inflammation and destruction of the supporting alveolar bone and periodontal ligament. The periodontal disease alters the morphologic features of bone in addition to reducing height. It leads to various patterns of bone loss, of which horizontal and vertical bone loss are the most common bone destruction patterns. Performing Intramarrrow penetration (IMP) in the surgical site creates a close spatial correlation between angiogenesis and bone formation. The vessel-rich medullary opening space would facilitate capillary sprouting and enhance vascular access into the surgical site. A local increase in bone morphogenetic proteins and other growth factors from the injured cortical surface, endosteal area, and wounded vessel area can enhance further new bone formation. Open flap debridement (OFD) is used in various periodontal flap techniques with intrasulcular incisions and is used to treat bony defects. Hyaluronic acid (HA), a naturally occurring polysaccharide, is regarded as an essential component of the extracellular matrix in connective tissues of the human body. HA has been extensively used in dentistry, especially in periodontology, due to its bacteriostatic, fungistatic, anti-inflammatory, anti-edematous, osteoinductive, and pro-angiogenic properties.  These studies indicate that HA speeds up the wound healing process and promotes regeneration by maintaining the viability of oral fibroblasts, increasing their proliferative and migratory abilities, and enhancing the expression of genes encoding type III collagen .Thus, the present study aims to evaluate the efficacy of bone formation in horizontal bony defects with Intramarrow penetration clinically and radiographically with and without Hyaluronic acid.